Polyolefins such as polyethylene and polypropylene have excellent molding properties, and they have been conventionally used widely as engineering plastics.
In the use of polyolefins as engineering plastics, products molded from the polyolefins are applied on their engaged portions with greases or the like to increase various properties of the molded products, such as slipperiness, sliding properties and abrasion resistance. Greases are generally prepared by adding a rust-preventing agent, a high-pressure lubricant, an antistatic agent, an anti-corrosive agent, etc. to a base oil having been previously treated with a viscosity builder to have a desired viscosity. Examples of the viscosity builders used herein include alkali metal soap, bentonite and silica gel. Greases are generally classified into lithium grease, benton grease, etc. depending on the kind of the viscosity builder. Since the greases contain various components in addition to the base oil as described above, the engineering plastics to be brought into contact with the greases are required to have properties different from the ordinary oil resistance. For example, lithium grease uses lithium soap as the viscosity builder, and this lithium soap is highly basic, so that the engineering plastic to be brought into contact with the lithium soap is required to show resistance to oils under basic atmosphere. However, polyolefins conventionally used are not always high in resistance to greases.
For improving the grease resistance of the polyolefins used for such purpose and further improving other properties such as heat resistance and rigidity, a method of increasing crystallinity of the polyolefins has been used. In order to increase the crystallinity of the polyolefins, there are known, for example, a method of adding a nucleating agent and a method of slowly cooling the polyolefin in the molten state, but the effects given by those methods are not sufficient.
By the way, it has been reported that a copolymer obtained by copolymerizing ethylene with a bulky monomer is much more improved in various properties such as heat resistance as compared with conventional polyolefins (see: U.S. Pat. No. 2,883,372, Japanese Patent Publication No. 46(1971)-14910, etc.).
Based on such finding that a cycloolefin random copolymer obtained by copolymerizing ethylene and a cycloolefin used as the bulky monomer is excellent in heat resistance, aging resistance, solvent resistance, dielectric properties and rigidity, the present inventor has applied for patents on random copolymers obtained by copolymerizing ethylene and specific cycloolefins (see: Japanese Patent Laid-open Publications No. 60(1985)-168708, No. 61 (1986)-120816, No. 61(1986)-115912, No. 61(1986)-115916, No. 61(1986)-271308, No. 61(1986)-272216, No. 62(1987)-252406 and No. 62(1987)-252407).
The present inventor has found that addition of specific amounts of a specific elastomer (or a crystalline polyolefin) and a polyamide resin to the above-mentioned cycloolefin resins makes it possible to remarkably improve the grease resistance of the molded products, without deteriorating the excellent properties of the cycloolefin resins, and accomplished the invention.